The isolation and characterization of the multiple forms of monoamine oxidase (MAO) were studied using SDS-polyacrylamide gel electrophoresis to determine the molecular weights of the different forms of the enzyme. The molecular weight of three of the forms appeared to be approximately 180,000, 70,000 and 10,000. The enzymic forms are being further characterized using affinity chromatography and electron spin resonance techniques (ESR). Using radio assay and ESR methods, blood platelet MAO derived from schizophrenic and control populations are being investigated. MAO derived from infant rat brains are being compared to that of adults using immunological procedures in order to ascertain possible developmental characteristics of the multiple forms of the enzyme.